The inventor has previously described a movement measuring apparatus referred to as CODA (see Mitchelson, D. L. 1975): Non-photographic techniques for movement analysis; in: Grieve, D. W. et al. Techniques for the analysis of human movement. Lepus, London; and Mitchelson, D. L. (1979): Bioengineering in motor function assessment and therapy; and in: Progress in Stroke Research, pp. 117-124. Ed. Greenhalgh, R. M. Clifford Rose, F. Pitman Medical, London.).
In such apparatus' landmarks were used in the form of LED's (light emitting diodes) which could be pulsed or modulated for distinguishing one landmark from another. Light impinging on multiple photodiode detector plates produced an analogue/digital signal indicative of the angular position of the LED landmark in the multiples photodiode observation field. The multiple photodiodes mounted on a plate were costly and the plate position had to be carefully calibrated to ensure reproducibility. The signal was a position-dependent signal and the accuracy of measurement obtainable was hence limited. The apparatus was costly and required skilled operatives.
There is also known a so-called SELSPOT system (made by Selective Electronic Company of Molndal Sweden) using LED landmarks but a single multiple electrode photodiode producing an entirely analogue signal dependant on the horizontal and vertical position of the landmark in an observation field. Ambient light could influence measurements. Where 3-dimensional measurement is required separate measuring units have to be sited carefully in their appropriate relative positions. Again the apparatus was costly, difficult to use and liable to produce inaccurate or not reproducible results.
It is the object of the invention to provide a movement measuring apparatus which can improve on the aforementioned apparatus as regards manufacturing cost, ease of use, accuracy and/or reproducibility.